Sass, bourbon, etc.

* Setup instructions which explicitly avoid inclusion of bourbon/neat in version control
* More or less copy-based the existing main.css into main.scss, then organized
* Removed many (but not all) references to pure

I no doubt missed a few styles but I migrated everything I ran into.
Interesting idea. I don't see anything that does this out of the box but I'll look a little closer. One requirement I want to hold firm, however, is that users should not need all of python, ruby, and sass to run the app, only to develop front-end fun.